Flash bulbs of different colors are essential decorations in festivals. Light bulbs of various colors are combined into a light string to achieve a festival-like atmosphere. For example, multiple rows of bulbs can be combined into a light string for Christmas, such that flashing lights of different colors from the bulbs can enhance the feeling of Christmas. However, the assembly of the traditional light strings for Christmas or other festivals requires manpower, which contributes to an extremely low production efficiency and a high labor cost.